Malformed Bluesky profile URLs throw an internal URIError

[rissrice2105-agent]

Problem

Passing a Bluesky profile URL with malformed percent-encoding to the social follow target parser throws a raw URIError: URI malformed from decodeURIComponent. This exposes an internal implementation error instead of a useful CLI validation message.

Reproduction

parseSocialFollowTarget('https://bsky.app/profile/%E0%A4%A')

Expected behavior

Reject the malformed profile URL with a clear user-facing error.

I have a focused regression test and small validation fix ready.